Effects of agitation and scale-up on drop size in turbulent dispersions: allowance for intermittency

Experimental and theoretical work has recently shown that classical drop size correlations have significant limitations. In particular, that work indicated a slow drift towards smaller drops when agitation is maintained, as well as smaller drops and faster break-up when scaling up at. constant power per unit volume. Moreover, the exponent on Weber number fell below -0.6. It was considered that the phenomenon of turbulent intermittency was the mechanism causing the limitations. Here, these ideas are explored farther using equations for stable drop size and drop break-up in intermittent turbulence, the latter being modelled by a multifractal spectrum. These equations are then successfully applied to new drop size measurements for two geometrically similar stirred tanks having different scales, giving further support for the need to consider the phenomenon of intermittency when modelling mixing processes in stirred tanks in the turbulent regime. (C) 2001 Elsevier Science Ltd. AH rights reserved.